Among the various vacuum pumps that are frequently used to realize a high vacuum environment are turbo-molecular pumps and threaded groove pumps.
Also amongst the vacuum apparatuses that are kept vacuum inside by the execution of an exhaust treatment using vacuum pumps such as turbo-molecular pumps or threaded groove pumps are chambers for semiconductor manufacturing apparatuses, electron microscope test chambers, surface analysis apparatuses, and micro-machining apparatuses.
Those vacuum pumps for realizing a high vacuum environment each have a casing that configures a casing equipped with an inlet port and an outlet port. A structure that brings about the exhaust function of such a vacuum pump is stored in the casing. The structure that brings about the exhaust function is constructed mainly with a rotating portion (a rotor portion) pivotally supported in a rotatable manner and a fixed portion (a stator portion) fixed with respect to the casing.
In a turbo-molecular pump, the rotating portion thereof is constituted by a rotating shaft and a rotating body fixed to this rotating shaft, wherein a plurality of stages of radial rotor blades (moving blades) are arranged in the rotating body. Also, a plurality of stator blades (stationary blades) are arranged alternately with the rotor blades, in the fixed portion.
In addition, a motor for rotating the rotating shaft at high speeds is provided. Rotating the rotating shaft at high speeds by the motor causes the interaction between the rotor blades and the stator blades to draw a gas from the inlet port and discharge the gas from the outlet port.
Incidentally, these vacuum pumps such as turbo-molecular pumps and threaded groove pumps are each configured to introduce from the inlet port an exhaust gas that contains particles generated within a vacuum container (e.g., particles of several μ to several hundred μm), such as fine particles of reaction products generated in, for example, a chamber for a semiconductor manufacturing apparatus.
Some of the steps executed by the vacuum apparatus arranged in such a vacuum pump inevitably cause such suspended matters called particles to adhere in the form of products (deposits) on the inside of the vacuum pump. Moreover, in some cases the exhaust gas to be discharged as described above turns into a solid product in accordance with a sublimation curve (vapor pressure curve). The deposition and solidification of products are likely to occur especially in the vicinity of the outlet port where the pressure of the gas increases.
Although any problems might not occur while the vacuum pump is rotated, the gas remaining in the vacuum pump becomes cold as soon as the rotation of the vacuum pump is stopped, leading to a growth of the products and resulting in adhesion of the rotating body of the vacuum pump and the products.
Accumulation of the products in the vicinity of the outlet port narrows the gas flow path and increases the backpressure. As a result, the exhaust performance of the vacuum pump deteriorates significantly.
The rotating body of the vacuum pump is generally manufactured from a metallic material such as aluminum or an aluminum alloy and normally rotates at 20,000 rpm to 90,000 rpm. The peripheral velocity thereof at the edges of the rotor blades reaches 200 m/s to 400 m/s. This configuration causes the thermal expansion of the rotor portion of the vacuum pump (the rotor blades in particular) and the creep phenomena in which the rotor portion becomes deformed in the radial direction over time. The thermal expansion and creep phenomena of the vacuum pump are more prominent at the lower side of the rotating body (the outlet port side) than the upper side (the inlet port side), bringing the expanded rotating body into contact with the deposited products at the outlet port side in particular.
In a case where the apparatus arranged in the vacuum pump is a chamber for a semiconductor manufacturing apparatus, because the main raw material of the semiconductor manufacturing wafer is silicon, the deposited products might become harder than the rotating body manufactured from aluminum or an aluminum alloy. When the products come into contact with the rotating body that rotates at high speeds as described above, the rotating body with a lower hardness breaks, which, in the worst-case scenario leads to a breakdown of the vacuum pump.
When part of the vacuum pump comes into contact with the products deposited in the vicinity of the outlet port where the pressure or temperature of the gas is high, as described above, problems such as deterioration of the performance of the vacuum pump and damage to the rotor blades occur in the vacuum pump. In order to remove the adhered products, an overhaul needs to take place on a regular basis in which the apparatus is disassembled before being thoroughly cleaned.